1. Field of the Invention
The present invention relates to a light measuring apparatus capable of obtaining measurement data with a high signal-to-noise ratio by effectively decreasing noise light.
2. Description of the Related Art
A 1-molecule fluorometric analyzer using a confocal optical system needs a complex optical system. A complex optical system mentioned here is configured to be able to adjust an optical path in a confocal optical system, and to change combination of complex filters corresponding to various wavelengths.
Jpn. Pat. Appln. KOKAI Publication No. 7-244238 discloses a confocal scanning microscope, which does not require adjusting an optical path. In this invention, a wavelength of light from one set of variable wavelength laser light source is changed by using a wavelength select reflector, and it is unnecessary to change two or more laser light sources, and an optical path is free from displacement.
Bioluminescence and fluorescent light emitted from a living sample are generally very weak in most cases. A measuring apparatus based on a confocal optical microscope for measuring such a very weak light uses a highly sensitive photodetector, such as a photoelectric multiplier and avalanche photodiode (APD).
In the invention disclosed by the Jpn. Pat. Appln. KOKAI Publication No. 7-244238, laser beams other than one of a necessary wavelength is cut off, causing loss in the light intensity, and the output is decreased. If the intensity of exciting laser beam is very weak, the intensity of fluorescence emitted from a sample becomes very weak. Thus, it is necessary to increase the photodetector sensitivity, but noise light is also amplified together with signal light.
Noise light includes light generated inside a measuring apparatus, in addition to disturbance light. For example, in a light measuring apparatus which measures a very weak light emitted from a living sample at a single molecule level in solution by using more than one light source, it is necessary to incorporate optical elements in a measuring optical path, such as a pinhole and a filter, to reduce light to a very small area and to detect light with high sensitivity, and it is necessary to adjust the positions of these optical elements with high accuracy.
Generally, the adjustment of the positions of these optical elements is automatically performed by detecting the coordinates of the positions by using a light position detector provided in each optical element. When detecting a very weak light from a sample by using a highly sensitive photodetector, a light beam emitted from a light source that is incorporated inside the light position detector is also detected by the photodetector used for measurement, and this may affect measured data as noise.